Electrodeposition of nickel



Mme- United States Patent 'Ofifice 2,9865 Patented May 30, 1961 ELECTRODEPOSITION OF NICKEL Bernard -P. Martin, Cleveland Heights, Ohio, assignor to The McGean Chemical Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed July 27,1959, Ser. No. 829,493

16 Claims. (Cl. 204-49) This invention pertains to plating solutions and processes employing them in the electrodeposition of nickel, and more particularly to improved plating solutions and processes in which certain organic brighteners of the coumarin type are employed.

It has heretofore been proposed to employ coumarin as an addition agent in aqueous acidic nickel plating baths. While coumarin alone as an addition to a standard Watts type nickel plating bath produces only a matte or semibright deposit, the nickel deposit produced in such a bath has excellent leveling or filling properties and ease of buifability. The use of coumarin has also been considered to provide advantages over organic brighteners which contain sulfur in their composition, for the reason that nickel deposits produced in the presence of such other brighteners are found to contain sulfur, co-deposited with the nickel, and this deposited sulfur is thought to be a source of corrosion, reducing the useful life of the deposit. Most of the' marin additive, so that oily droplets appear in the bath. The presence of the liquid form of coumarin, due to excess concentration, can cause degradation of the nickel deposit, manifesting itself in the form of pitting, streaking and possibly in poor adhesion if a subsequent nickel deposit is to be plated over the coumarin nickel deposit. A degradation of the nickel deposit is further found'in the use of coumarin where low cathode current density conditions obtain, producing a dark brown or grey stain which will not readily brighten up with bufling or with a subsequent bright nickel deposit. This is due to chemical decomposition of the coumarin itself to harmful deriva tives.

Frequent purification of the bath has thus been required and this is troublesome, expensive and can be time consuming; it is consequently objectionable to the plater' on these accounts. Various proposals have been made to ameliorate these difiiculties, as by the addition to the bath of extenders such as formaldehyde to postpone the time when purification must be done. This helps but-is not altogether satisfactory because the proper addition of formaldehyde is dependent largely on its rate of evaporation from the bath and this varies widely with different ambient conditions. This makes accurate control of the proper concentration of extender difficult to maintain practically. Moreover, excessive amounts of formaldehyde cause brittleness in the nickel deposit and substantially reduce the natural leveling power of the coumarin. The leveling characteristic of coumarin, of course, is one of the main reasons for employing this material in the first place. Further difiiculty has been encountered heretofore in the use of coumarin and the suggested substituted forms with respect to loss of leveling power of the bath when These advantages of leveling power, bufling ease and absence of sulfur in the'deposited nickel plate have, in part, made up for the fact that coumarin does not provide a bright deposit or one which is of uniform color where plating conditions vary materially as is almost always true in commercial practice. That is, the tolerance of coumarin containing baths to temperature, acidity and particularly to plating cathode current densities, is relatively poor. And although bufling is easier with deposits obtained from plating solutions to which coumarin has been added in comparison with gray nickel deposits, it still remains a fact that any bufiingadds to the expense of the item being plated, and it is accordingly the ultimate objective of most nickel plating processes to obtain a fullbright deposit, as plated, to eliminate the need for mechanical or electrical buffing before application of a final deposit, usually of chromium.

Owing to the shortcomings of coumarin itself in the respects above mentioned, numerous attempts have been made to provide supplemental corrective addition agents, or alternatively to find derivatives or substituted forms of coumarin, which will free the plating solutions from the drawbacks of the parent compound. Only limited success has been reported until now in this direction. For example, one of the principal problems with the use of coumarin and the heretofore suggested substituted forms thereof has been the necessity for frequent purification of the plating bath, either by continuous filtration or periodic treatment at very frequent intervals when operatingunder regular commercial plating conditions. One reason for the foregoing arises from the appearance in the plating solution of an oily, immiscible liquid phase due to the presence of an excess of coumarin in the bath, above its .solubility limit. This is primarily occasioned by the need or desirability of operating the bath at a temperature close to or above the melting point of the cousupplementary well-known or proprietary brighteners are incorporated to improve the brightness of the deposit obtained therefrom. Again it has been necessary, therefore, to counteract the loss of leveling power under the abovedescribed conditions by still further additions of certain organic leveling agents. This is at best a compromise, as the full leveling power of the coumarin itself'is seldom restored. In any event, this further addition introduces other complications and expense in preparing and maintaining the bath.

In accordance with the present invention it has been found that a remarkable improvement in the elimination of the difiiculties heretofore encounteredwithcoumarin in nickel plating baths is obtained through the use of certain substituted coumarin compounds of ,a particular class. These may be used alone in a standard aqueous acid bath or in conjunction with certain types of knownprimary and secondary brightening agents. The specific substituted coumarin compounds found to possess the unique properties herein disclosed are the lower hydroxyalkyl mono and poly-substituted derivatives, where the substitutions are made in the 5, 6, 7, or 8 numbered positions of the coumarin nucleus. The use of these derivatives results in a marked improvement in the brightness of the nickel deposit, without the use of supplemental brighteners, as compared to coumarin itself. In addition, the hydroxyalkyl coumarins provide a marked decrease'in purification requirements, as baths containing these com pounds may be operated for long periods without requiring the addition of extenders to avoid degradation of the nickel 'deposit. It has also been found that the novel hydroxyalkyl coumarin compounds are entirelycompatible with certain known brighteners of the primary type, these being the aryl sulfonamides or sulfonimides, and with sec-. ondary brighteners of the amino polyaryl methane types,- whereby the leveling properties of coumarin itself are fully maintained and even enhanced without adverse effect upon the brightness ofthe deposit.

The term lower hydroxyalkyl substituted coumarins is used herein to designate hydroxymethyl, hydroxyethyl and hydroxypropyl coumarin. As mentioned above, the substitutions may replace nuclear hydrogen atoms in one or more of positions 5, 6, 7 or 8 of the coumarin nucleus. On the basis of plating operations under commercial conditions so far conducted, hydroxymethyl coumarin, and more particularly the mono-substituted 6-hydroxymethyl coumarin, has proven most effective. It appears also that the hydroxyethyl and hydroxypropyl substituted for-ms, as well as the di-substituted and other poly-substituted forms are capable of producing good results. The chief difficulty at the present time with the poly-substituted compounds, as well as with the ethyl and propyl forms, is their ready availability and economical production, with the result that the mono hydroxymethyl coumarin definitely represents the preferred compound at the present time.

It may be noted here I have also found that the addition of certain haloalkyl substituted coumarins, in which the substituent radicals are attached in the 5, 6, 7 or 8 numbered positions in the coumarin nucleus as before, will produce results comparable with those of the hydroxyalkyl derivatives, but such results are obtained only after the bath has been allowed to stand for some time after preparation. Immediately after preparation of a bath containing, for example, chloromethyl coumarin, no useful plating results are obtained, whereas such bath after standing for a period of time gives excellent results. It is believed, therefore, that the change which takes place is one involving hydrolysis of the haloalkyl compound to the corresponding hydroxyalkyl one under the prevailing operating conditions. In any event, it seems clear that the unique results obtained in accordance with the invention are dependent on the hydroxyalkyl coumarin compounds, and that the haloalkyl compounds, as such, are not effective.

The amount of hydroxyalkyl coumarin present in solution need only be small to be elfective, and in general may range from as little as 0.05 gram per liter of solution to the upper limit of its solubility in the bath. The latter is not great but is definitely better than coumarin and many of the other substituted coumarin compounds, being on the order of 1.5 g./l. in the typical acid nickel bath. There is no objection to the use of this upper limit of hydroxyalkyl coumarin but economic factors, as well as optimum operating performance, dictate that the amount normally be substantially less. With non-agitated operation obtaining in the plating tank, optimum concen-' tration of the additive runs from about 0.1 to 0.6 g./l., with the best results being obtained at about 0.4 g./l. Under conditions of air or mechanical agitation in the bath, the concentrations used are preferably somewhat lower, usually around 0.2 g./l.

The major constituents of the basic nickel plating bath with which the novel additives may be employed are, of course, the nickel ion supplying compound or compounds and the water in which they are dissolved. These nickel compounds may be any of the commonly employed soluble salts such as nickel sulfate and nickel chloride or, if desired, nickel sulfamate or nickel fluoroborate. Generally a combination of nickel sulfate and chloride salts is used, and the concentrations of these run, respectively, between 180 to 400 and 8 to 120 grams per liter of bath solution.

A buffering agent, such as boric acid, is also contained in solution. Concentrations of 8 to 50 g./l. of boric acid are desirable. Generally, where agitation is not employed, an anti-pitter of the sulfated long-chain aliphatic alcohol type, e.g. sodium lauryl sulfate, is also included, the amount of this being from 0.025 to 0.2 g./l.

' Excellent semi-bright nickel deposits are obtained from a standard bath of the Watts type containing as the only brightening or leveling agent a hydroxyalkyl coumarin of the invention. The following is typical of the composition of such a bath:

The acidity of the bath may range from pH 2.5 to 4.8, while optimum conditions are obtained at about pH 4.2. The bath operates entirely satisfactorily within the usual range of plating temperatures, particularly in the upper range commonly preferred. Any temperature from 40 to 70 C. is satisfactory, although 55 C. is usually optimum. Cathode current densities are not critical and may range anywhere within the values usually encountered of from 5 to amperes per sq. ft.

In the case of 6-hydroxymethyl coumarin, outstanding improvement is obtained by the use of this material in a nickel plating bath of the type above described, as compared with other previously suggested coumarin compounds. Thus, the hydroxymethyl coumarin produces a nickel deposit of luster approaching that of full brightness, as compared to a finish of a cloudy or milky-bright order only for the coumarin compounds heretofore proposed. Not only is the nickel deposit which results from the use of the hydroxymethyl coumarin of a higher order of luster, but it is more uniform over the article, and is maintained over a wider variation of cathode current densitim. Coumarin itself, under the same conditions, produces a cloudy, semi-bright deposit at best, even at the lower cathode current densities, and this becomes matte or almost matte when the upper cathode current density values are encountered.

Since the deposit obtained when using hydroxymethyl coumarin as the only brightening additive in the bath is essentially brighter and more uniform, the deposit is suitable as a base for a subsequent bright nickel deposit, without any intermediate buffing operations, in a duplex system of nickel plating. As those in this art are well aware, the duplex system consists in applying an initial nickel deposit which, as the term is used herein, is produced in a bath free from sulfur-containing brightener agents. That initial plate is then followed by a second plate produced in a solution containing the usual fullbrightening sulfur-containing agents. This duplex plating provides advantages of greater corrosion resistance in the protective nickel plate, giving added life to the plated article. Deposits formed from the hydroxymethyl coumarin bath show a very high order of corrosion resistance. Moreover they exhibit excellent ductility.

The leveling power of hydroxymethyl coumarin is outstanding and is generally better than that of the parent coumarin compound itself, the improvement being on the order of at least 10%. This is quite the reverse of results obtained with other, heretofore proposed coumarin compounds. Further, hydroxymethyl coumarin does not form an oily, immiscible phase, even when present in excess concentration in a nickel bath at any possible operating temperature, as its melting point is on the order of 150 C. Nor does it form oily decomposition products. Baths employing hydroxymethyl coumarin have been consistently operated, Without modification, for at least twice as long a period as heretofore possible with other coumarin compounds before purification steps become necessary.

' ll of the hydroxyalkyl coumarin compounds here disclosed have the advantage of relatively high melting points, substantially higherthan coumarin itself, so that even if they are added in excess of their solubility in the bath, no oily accumulation or phase is produced.

7 The hydroxyalkyl coumarin compounds herein disclosed are-foundto be entirely compatible with certain standard bright nickel plating baths employing primary and secondary brighteners of well-known type. Thus it is found that a bright nickel bath containing a primary brightener of the aryl sulfonamide or sulfonimide type, more especially the benzene and naphthalene compounds, together with a secondary brightener of the amino polyaryl methane type, results in full-bright deposits of greatly improved leveling properties. Saccharin has been found particularly effective as a primary brightener. On the other hand, the naphthalene sulfonic acids commonly used as such primary brighteners are not as good as saccharin, as the brightness of the deposit becomes fogged. Suitable secondary brighteners within the class just mentioned included fuchsin, reduced fuchsin, p,p methylene dianiline and 2-2, 4-4 tetramino 5-5 dimethyl diphenylmethane. The proper concentrations of the primary brighteners range from about 0.5 to 25 g./l., with the higher concentrations technically posible but generally not desirable from the economic standpoint. Usually from 0.5 to 5.0 g./l. gives best results. In the case of the secondary brighteners, the amount employed should be at least 2 milligrams per liter of bath solution, and may go as high as 100 milligrams per liter. Preferably, however, an upper limit of 50 milligrams should-be observed.

The uniqueness of the hydroxyalkyl coumarin compounds in affording the improvements noted hereinabove is effectively demonstrated by tests made using coumarin compounds closely similar from chemical composition standpoint. For example, a methyl coumarin, when used in the standard Watts nickel plating bath, produces no noticeable effect whatever upon the deposit obtained. Similarly, a hydroxy coumarin in such a bath shows at most a slight grain refining action which, however, is of little significance. Acetoxymethyl coumarin produces some leveling which, however, is materially below that of the parent coumarin itself and is not of such order as to be satisfactory. No noticeable improvement in brightness of the deposit is obtained by the use of this compound. Chloromethyl coumarin itself, as mentioned hereinaoove, produces no significant effect upon the plated deposit, unless the plating solution containing this material is allowed to stand for some period of time. Then the results obtained are directly comparable with those of hydroxymethyl coumarin, and this is believed due to hydrolysis of the halo-substituted compound to the hydroxy compound. Formyl coumarin produces some increase in leveling power of the basic bath, but this does not equal that of coumarin itself. It also shows some improvement in brightness of the deposit but again the results obtained are distinctly inferior and of a different order entirely from that obtained in the use of the hydroxyalkyl compounds.

What is claimed is:

1. An electroplating bath for the production of bright, level deposits of nickel, which comprises an aqueous acid nickel electrolyte solution containing a predominating amount of a soluble nickel salt and having incorporated therein a leveling and brightening agent selected from the group consisting of hydroxymethyl, hydroxyethyl and hydroxypropyl coumarin, wherein the substituent groups in said agent are attached to the coumarin nucleus in at least one of the 5, 6, 7 and 8 positions, said agent being present in solution in effective amount ranging from at least 0.05 -g./l. to the limit of its solubility.

2. A nickel plating bath solution as defined in claim 1, wherein said leveling and brightening agent is present in amount from 0.2 to 0.6 g./l.

3. A nickel plating bath solution as defined in claim 1, wherein said a-gent is hydroxymethyl coumarin.

4. A nickel plating bath solution as defined in claim 3, wherein said agent is present in amount from 0.2 to 0.6 g./l.

5. A nickel plating bath for the electroplating of nickel in bright, level deposits, which comprises, per liter of solution:

Grams NiSO 6H O 280 NiCl -6H O 60 H BO 45 Sodium lauryl sulfate 0.1 Saccharin 0.005 6-hydroxymethyl coumarin 0.4

6. An electroplating bath for the production of bright, level deposits of nickel, which comprises an aqueous acid nickel electrolyte solution containing a predominating amount of a soluble nickel salt and minor amounts of cooperating addition agents, one of said agents being selected from the group consisting of the benzene and naphthalene sulfonamides and sulfonimides and being present in amount from about 0.5 to 25.0 g./l., a second agent selected from the group of amino polyaryl methanes consisting of fuchsin, reduced fuchsin, p,p methylene dianiline, and 2-2, 4-4 tetramino 5-5 dimethyl diphenylmethane in amount from 2 to milligrams per liter of solution, and a third agent selected from the group consisting of hydroxymethyl, hydroxyethyl and hydroxypropyl coumarin wherein the substituent groups are attached to the coumarin nucleus in at least one of the 5, 6, 7 and 8 positions, said third agent being present in amount from about 0.05 g./l. to the limit of its solubility.

7. A nickel plating bath solution as defined in claim 6, wherein said third agent is hydroxymethyl coumarin.

8. A nickel plating bath solution as defined in claim 7, wherein said third agent is present in amount from 0.2 to 0.6 g./l.

9. A nickel plating bath solution as defined in claim 8, which further contains about 45 g./l. of boric acid as a buffering agent and about0.1 g./l. of sodium lauryl sulfate as an anti-pitter.

10. The process of producing a ductile bright nickel deposit having good leveling characteristics, which comprises electrodepositing nickel from an aqueous acid bath containing the nickel mainly in the form of a soluble nickel salt, and a leveling and brightening agent selected from the group consisting of hydroxymethyl, hydroxyethyl and hydroxypropyl coumarin wherein the substituent groups are attached to the coumarin nucleus in at least one of the 5, 6, 7 and 8 positions, said agent being present in amount from at least 0.05 g./l. to the limit of its solubility, said process being carried out at a temperature of 40 to 70 C. and at a cathode current density of 5 to amperes per square foot, the pH of said bath lying in the range of 2.5 to 4.8.

11. The process as defined in claim 10, wherein said agent is hydroxymethyl coumarin.

12. The process as defined in claim 11, wherein said hydroxymethyl coumarin is present in amount from 0.2 to 0.6 g./l.

13. The process of producing a ductile full-bright nickel deposit having superior leveling properties, which comprises electrodepositing nickel from an aqueous acid bath containing the nickel mainly in the form of a soluble nickel salt, together with cooperating addition agents, one of said agents being selected from the group consisting of the benzene and naphthalene sulfonamides and sulfonimides and being present in amount of 0.5 to 25.0 g./l., a second agent selected from the group of amino polyaryl methanes consisting of fuchsin, reduced fuchsin, p,p methylene dianiline and 2-2, 4-4' tetramino 5-5 dimethyl diphenylmethane in amount from 2 to 100 milligrams per liter of solution, and a third agent selected from the group consisting of hydroxymethyl, hydroxyethyl and hydroxypropyl coumarin wherein the substituent groups are attached to the coumarin nucleus in at least one of the 5, 6, 7 and 8 positions, said third agent being present in amount of 0.05 g./l. to the limit of its solubility, said process being carried out at a temperature of 40 to 70 C. and at a cathode current density of 5 to 150 amperes per square foot, the pH of said bath being maintained at 2.5 to 4.8.

, 14. The process defined in claim 13, wherein said bath further contains from 8 to 50 g./l. of boric acid as a buffer and from 0.025 to 0.2 g./l. of sodium lauryl sulfate as an anti-pitter.

15. The process defined in claim 13, wherein said third agent is hydroxymethyl coumarin.

16. The process defined in claim 15, wherein said agent is present in amount from 0.2 to 0.6 g./l.

References Cited in the file of this patene UNITED STATES PATENTS 

1. A PROCES FOR DEXOYGENATING A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM WHICH COMPRISE: ANODICALLY DISSOLVING AN OXYGEN CONTAMINATED ANODE FORMED FROM SAID METAL INTO AN ELECTROYLTE ESSENTIALLY CONSISTING OF MOLTEN MAGNESIUM CHLORIDE, SAID ANODE HAVING LESS THAN 10% OXYGEN THEREIN, WHEREBY METAL AND OXYGEN DISSOLVE INTO THE ELECTROLYTE IN CHEMICALLY COMBINED FORMS, REMOVING THE COMBINED OXGEN FROM THE ELECTROLYTE BY CONVERSION OF THE OXYGEN INTO A GASIFORM PRODUCT WHICH EXCAPES FROM THE ELECTROLYTE, REMOVING THE VOLATILIZED GASIFORM PRODUCT FROM ABOVE THE SURFACE OF SAID ELECTROLYTE, AND SIMULTANEOUSLY CONTINUOUSLY PLATING SAID METAL OUT IN MASSIVE FORM AT THE CATHODE. 